1. Field of the Invention
This invention relates to a head suspension assembly used in a disk device and the disk device provided with the same.
2. Description of the Related Art
In recent years, disk devices, such as magnetic disk devices, optical disk devices, etc., have been widely used as external recording devices of computers and image recording devices. A magnetic disk device as an example of a disk device comprises a magnetic disk, a spindle motor, a magnetic head, and a carriage assembly, which are arranged in a case. The spindle motor supports and rotates the disk. The magnetic head is used to write and read information to and from the disk. The carriage assembly supports the magnetic head for movement with respect to the magnetic disk. The carriage assembly comprises an arm attached to a suspension and a head portion provided on the slider. The head portion includes a reproducing element for reading and a recording element for writing.
The slider has a facing surface that faces a recording surface of the magnetic disk. The suspension applies a given head load bound for a magnetic recording layer of the disk to the slider. When the magnetic disk device is operating, an air current is generated between the rotating disk and the slider. Based on the principle of air-fluid lubrication, the facing surface of the slider is subjected to a force that causes the slider to fly above the recording surface of the disk. The slider is lifted with a fixed gap kept above the recording surface of the magnetic disk by balancing the flying force and the head load. As described in Jpn. Pat. Appln. KOKAI Publication No. 2001-283549, for example, the flying height, flying posture, and flying height under reduced pressure of the slider can be adjusted by properly shaping the irregularities of the facing surface that faces the disk.
Sliders have recently been made smaller and smaller. Slider sizes are standardized by International Disk Drive Equipment and Materials Association (IDEMA) standards. The sliders are named mini-sliders (100% sliders), micro-sliders (70% slider), nano-sliders (50% sliders), pico-sliders (30% sliders), and femto-sliders (20% sliders) in the descending order of size.
For example, the femto-sliders (0.85 mm by 0.7 mm by 0.23 mm) are smaller than the currently prevailing pico-sliders (1.25 mm by 1 mm by 0.3 mm). Magnetic heads are collectively manufactured by thin film processes. If the slider size is reduced, therefore, the yield of production of the magnetic heads can be increased with use of the same processes, so that the manufacturing costs can be lowered. Miniaturization of the sliders can improve the performance of the magnetic heads to follow up the irregularities of the magnetic disk surface. Further, the mass of the distal end portion of a head actuator is reduced, so that improvement of the seek speed can be expected. If the slider width is lessened, moreover, a recording region of the disk surface can be enlarged.
If the area of the facing surfaces of the sliders narrows with the miniaturization of the sliders, however, the following problems are expected to arise.
(1) The flying force of the magnetic heads is reduced, so that the head load cannot be supported, and the magnetic heads inevitably touch the disk surfaces.
(2) The head load cannot be supported, so that the loading posture of the magnetic heads collapses.
Conventionally, a measure to lessen the head load in proportion to the miniaturization of the sliders is used to solve these problems. According to recently predominant systems, the head load is also lessened if the sliders are downsized from pico-sliders to femto-sliders. If a femto-slider is used in a 2.5-inch type hard disk drive for mobile equipment, for example, the head load is believed to have its upper limit at 19.6 mN (2 gf).
Shock resistance (lift-off G or maximum leaving acceleration) Amax of the suspension can be given byAmax=F/(M+m),  (1)where m is the mass of the slider. The shock resistance Amax depends on a suspension mass (equivalent mass in terms of dimple position) M and a head load F. Therefore, the shock resistance Amax is low if the head load F is low.
If the head load is lessened in proportion to the miniaturization of the slider, the suspension and the slider are liable to bounce off the magnetic disk when the disk device is shocked. When the bounced slider returns to its original position, it may possibly run against the disk, thereby damaging recording data. Thus, the reduction of the head load lowers the shock resistance performance of the disk device.
If the slider is reduced in size so that its mass lessens, m in the aforesaid equation (1) becomes smaller, resulting in an improvement in the shock resistance. However, a bouncing force that is generated when an impact is applied is greatly influenced by the equivalent mass of the suspension. In practice, therefore, the reduction of the slider mass is hardly conducive to the improvement in the shock resistance. Thus, the reduction of the head load that is involved in the miniaturization of the slider lowers the shock resistance, possibly degrading the reliability of the disk device.